CO2-plasma surface treatment of graphite sheet electrodes for detection of chloramphenicol, ciprofloxacin and sulphanilamide.

Graphite sheet (GS) electrodes are flexible and versatile substrates for sensing electrochemical; however, their use has been limited to incorporate (bio)chemical modifiers. Herein, we demonstrated that a cold (low temperature) CO2 plasma treatment of GS electrodes provides a substantial improvement of the electrochemical activity of these electrodes due to the increased structural defects on the GS surface as revealed by Raman spectroscopy (ID/IG ratio), and scanning electron microscopy images. XPS analyses confirmed the formation of oxygenated functional groups at the GS surface after the plasma treatment that are intrinsically related to the substantial increase in the electron transfer coefficient (K0 values increased from 1.46 × 10-6 to 2.09 × 10-3 cm s-1) and with reduction of the resistance to charge transfer (from 129.8 to 0.251 kΩ). The improved electrochemical activity of CO2-GS electrodes was checked for the detection of emerging contaminant species, such as chloramphenicol (CHL), ciprofloxacin (CIP) and sulphanilamide (SUL) antibiotics, at around + 0.15, + 1.10 and + 0.85 V (versus Ag/AgCl), respectively, by square wave voltammetry. Limit of detection values in the submicromolar range were achieved for CHL (0.08 µmol L-1), CIP (0.01 µmol L-1) and SFL (0.11 µmol L-1), which enabled the sensor to be successfully applied to natural waters and urine samples (recovery values from 85 to 119%). The CO2-GS electrode is highly stable and inexpensive ($0.09 each sensor) and can be easily inserted in portable 3D printed cells for environmental on-site analyses.

Stainless steel and polyethylene surfaces functionalized with silver nanoparticles.

The antimicrobial effects of a stainless steel surface and a polyethylene surface functionalized with silver nanoparticles on the adhesion of different bacteria and the changes in physical and chemical characteristics of these surfaces that influence biofilm formation were evaluated. The functionalized surfaces of polyethylene and stainless steel were more hydrophobic than the control ones. The bacterial surfaces were hydrophilic. The adhesion of all bacteria was thermodynamically favorable (ΔGadhesion<0) on all surfaces functionalized and control. The numbers of adhered cells of Staphylococcus aureus, Escherichia coli, and Pseudomonas fluorescens were not significantly different (p > 0.05) between the control and functionalized surfaces, reaching values compatible with biofilm formation. Analysis of atomic absorption spectrometry using water and reconstituted skim milk as simulants showed no release of Ag from the functionalized surfaces. In conclusion, the surfaces that were functionalized with silver nanoparticles were modified in hydrophobicity, roughness, and did not avoid bacterial adhesion. Additional studies of surfaces functionalized with silver nanoparticles should be conducted addressing the adsorption technique of silver nanoparticles on the stainless steel surface as well as in the preparation of the polyethylene surface to allow the contact of microorganism with the antimicrobial agent.